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Obesogens beyond Vertebrates: Lipid Perturbation by Tributyltin in the Crustacean Daphnia magna.

Jordão R, Casas J, Fabrias G, Campos B, Piña B, Lemos MF, Soares AM, Tauler R, Barata C - Environ. Health Perspect. (2015)

Bottom Line: The analysis of obesogenic effects in invertebrates is limited by our poor knowledge of the regulatory pathways of lipid metabolism.TBT's disruptive effects translated into a lower fitness for offspring and adults.These findings indicate the presence of obesogenic effects in a nonvertebrate species.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research (IDAEA), Spanish Research Council (IDAEA, CSIC), Barcelona, Spain.

ABSTRACT

Background: The analysis of obesogenic effects in invertebrates is limited by our poor knowledge of the regulatory pathways of lipid metabolism. Recent data from the crustacean Daphnia magna points to three signaling hormonal pathways related to the molting and reproductive cycles [retinoic X receptor (RXR), juvenile hormone (JH), and ecdysone] as putative targets for exogenous obesogens.

Objective: The present study addresses the disruptive effects of the model obesogen tributyltin (TBT) on the lipid homeostasis in Daphnia during the molting and reproductive cycle, its genetic control, and health consequences of its disruption.

Methods: D. magna individuals were exposed to low and high levels of TBT. Reproductive effects were assessed by Life History analysis methods. Quantitative and qualitative changes in lipid droplets during molting and the reproductive cycle were studied using Nile red staining. Lipid composition and dynamics were analyzed by ultra-performance liquid chromatography coupled to a time-of-flight mass spectrometer. Relative abundances of mRNA from different genes related to RXR, ecdysone, and JH signaling pathways were studied by qRT-PCR.

Results and conclusions: TBT disrupted the dynamics of neutral lipids, impairing the transfer of triacylglycerols to eggs and hence promoting their accumulation in adult individuals. TBT's disruptive effects translated into a lower fitness for offspring and adults. Co-regulation of gene transcripts suggests that TBT activates the ecdysone, JH, and RXR receptor signaling pathways, presumably through the already proposed interaction with RXR. These findings indicate the presence of obesogenic effects in a nonvertebrate species.

No MeSH data available.


Lipidomic profiles of major lipid classes (mean ± SE; n = 3) in control, TBT L, and TBT H treatment groups during the adolescent instar in females at 0, 8, 16, and 24 hr, in de-brooded females just after the fourth molt (48 hr), and in eggs. Abbreviations: TG, triacylglycerols; DG, diacylglycerols; CE, cholesterylesters; PC, phosphocholines; LPC, lysophosphatidylcholine; SM, sphingolipids; PE, phosphatidylethanolamine; PS, phosphatidylserine; PI, phosphatidylinositol.
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f2: Lipidomic profiles of major lipid classes (mean ± SE; n = 3) in control, TBT L, and TBT H treatment groups during the adolescent instar in females at 0, 8, 16, and 24 hr, in de-brooded females just after the fourth molt (48 hr), and in eggs. Abbreviations: TG, triacylglycerols; DG, diacylglycerols; CE, cholesterylesters; PC, phosphocholines; LPC, lysophosphatidylcholine; SM, sphingolipids; PE, phosphatidylethanolamine; PS, phosphatidylserine; PI, phosphatidylinositol.

Mentions: Changes in the lipidome across TBT treatments. Changes in the lipid content of D. magna juveniles, unexposed (control) or exposed to TBT L or TBT H during the adolescent instar, are shown in Figure 2 (for supporting statistics, see Supplemental Material, Table S5). The sampling time significantly affected (p < 0.05) the levels of the nine studied lipid classes within and across TBT concentrations (time and time × treatment effects; see Supplemental Material, Table S5). Levels of TG, DG, CE, and PC in adolescent females increased at the beginning of the instar, peaking at 16–24 hr, and decreased afterward, reaching the lowest levels just after molting in de-brooded females (48 hr). Levels of TG showed the greatest changes, increasing up to 6-fold in control females. Levels of PE, PS, PI, and SM increased during the adolescent instar, usually reaching their highest levels 24 hr after molting. In contrast, LPC showed little variation during the adolescent instar. Exposure to TBT affected levels of most lipid classes, with the exception of LPC. Levels of TG, CE, and PC were reduced by TBT exposure during the first 24 hr of the instar, but they showed increased residual levels just after molting in de-brooded females. Levels of DG in females exposed to TBT were always higher than those of controls. TBT also reduced the overall levels of lipids belonging to classes of SM, PE, PS, and PI. Unexposed eggs showed levels of TG and CE comparable to the highest levels observed in adult females, whereas PS levels were about 1.5-fold higher than those of de-brooded females just after molting. In contrast, levels of DG, PC, LPC, SM, PE, and PI were lower in eggs than in adults. Exposure to TBT reduced TG, PC, and PS levels in eggs relative to controls, and dramatically increased CE levels (Figure 2). Clustering analysis of individual lipids using K-Means identified four main clusters (see Supplemental Material, Figure S2), from which two of them (clusters 2 and 3) were particularly enriched with TG, DG, and CE. Cluster 2 included the most unsaturated TG (see Supplemental Material, Figure S3), which were mostly transferred to eggs. Within this cluster, 10 of 26 lipid species had a total fatty acyl chain length ≥ 52 and a total number of unsaturated bonds ≥ 4; thus, they could include the polyunsaturated fatty acids (PUFA) arachidonic acid (20:4) and eicosapentanoic acid (20:5) combined with two palmitic acids (16:0). Levels of these TG increased in controls through two-thirds of the instar (i.e., 24 hr), when they were mostly allocated to eggs; their levels were consequently reduced to negligible levels in de-brooded females just after molting (48 hr; see Supplemental Material, Figure S3, top). TBT H disrupted this process, making females reach peak levels earlier, maintaining high levels even after molting, and reducing the amount of these lipids allocated to eggs. Lipid profiles in eggs and females exposed to TBT L showed intermediate levels of disruption. Cluster 3 included the less unsaturated TG (see Supplemental Material, Figure S3, bottom) that were only partially (60%) transferred to eggs in control females. Exposure to TBT (either at the high or low dose) decreased the maximal attained levels of these lipids, and notably reduced their transfer to the eggs (see Supplemental Material, Figure S3, bottom).


Obesogens beyond Vertebrates: Lipid Perturbation by Tributyltin in the Crustacean Daphnia magna.

Jordão R, Casas J, Fabrias G, Campos B, Piña B, Lemos MF, Soares AM, Tauler R, Barata C - Environ. Health Perspect. (2015)

Lipidomic profiles of major lipid classes (mean ± SE; n = 3) in control, TBT L, and TBT H treatment groups during the adolescent instar in females at 0, 8, 16, and 24 hr, in de-brooded females just after the fourth molt (48 hr), and in eggs. Abbreviations: TG, triacylglycerols; DG, diacylglycerols; CE, cholesterylesters; PC, phosphocholines; LPC, lysophosphatidylcholine; SM, sphingolipids; PE, phosphatidylethanolamine; PS, phosphatidylserine; PI, phosphatidylinositol.
© Copyright Policy - public-domain
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4529017&req=5

f2: Lipidomic profiles of major lipid classes (mean ± SE; n = 3) in control, TBT L, and TBT H treatment groups during the adolescent instar in females at 0, 8, 16, and 24 hr, in de-brooded females just after the fourth molt (48 hr), and in eggs. Abbreviations: TG, triacylglycerols; DG, diacylglycerols; CE, cholesterylesters; PC, phosphocholines; LPC, lysophosphatidylcholine; SM, sphingolipids; PE, phosphatidylethanolamine; PS, phosphatidylserine; PI, phosphatidylinositol.
Mentions: Changes in the lipidome across TBT treatments. Changes in the lipid content of D. magna juveniles, unexposed (control) or exposed to TBT L or TBT H during the adolescent instar, are shown in Figure 2 (for supporting statistics, see Supplemental Material, Table S5). The sampling time significantly affected (p < 0.05) the levels of the nine studied lipid classes within and across TBT concentrations (time and time × treatment effects; see Supplemental Material, Table S5). Levels of TG, DG, CE, and PC in adolescent females increased at the beginning of the instar, peaking at 16–24 hr, and decreased afterward, reaching the lowest levels just after molting in de-brooded females (48 hr). Levels of TG showed the greatest changes, increasing up to 6-fold in control females. Levels of PE, PS, PI, and SM increased during the adolescent instar, usually reaching their highest levels 24 hr after molting. In contrast, LPC showed little variation during the adolescent instar. Exposure to TBT affected levels of most lipid classes, with the exception of LPC. Levels of TG, CE, and PC were reduced by TBT exposure during the first 24 hr of the instar, but they showed increased residual levels just after molting in de-brooded females. Levels of DG in females exposed to TBT were always higher than those of controls. TBT also reduced the overall levels of lipids belonging to classes of SM, PE, PS, and PI. Unexposed eggs showed levels of TG and CE comparable to the highest levels observed in adult females, whereas PS levels were about 1.5-fold higher than those of de-brooded females just after molting. In contrast, levels of DG, PC, LPC, SM, PE, and PI were lower in eggs than in adults. Exposure to TBT reduced TG, PC, and PS levels in eggs relative to controls, and dramatically increased CE levels (Figure 2). Clustering analysis of individual lipids using K-Means identified four main clusters (see Supplemental Material, Figure S2), from which two of them (clusters 2 and 3) were particularly enriched with TG, DG, and CE. Cluster 2 included the most unsaturated TG (see Supplemental Material, Figure S3), which were mostly transferred to eggs. Within this cluster, 10 of 26 lipid species had a total fatty acyl chain length ≥ 52 and a total number of unsaturated bonds ≥ 4; thus, they could include the polyunsaturated fatty acids (PUFA) arachidonic acid (20:4) and eicosapentanoic acid (20:5) combined with two palmitic acids (16:0). Levels of these TG increased in controls through two-thirds of the instar (i.e., 24 hr), when they were mostly allocated to eggs; their levels were consequently reduced to negligible levels in de-brooded females just after molting (48 hr; see Supplemental Material, Figure S3, top). TBT H disrupted this process, making females reach peak levels earlier, maintaining high levels even after molting, and reducing the amount of these lipids allocated to eggs. Lipid profiles in eggs and females exposed to TBT L showed intermediate levels of disruption. Cluster 3 included the less unsaturated TG (see Supplemental Material, Figure S3, bottom) that were only partially (60%) transferred to eggs in control females. Exposure to TBT (either at the high or low dose) decreased the maximal attained levels of these lipids, and notably reduced their transfer to the eggs (see Supplemental Material, Figure S3, bottom).

Bottom Line: The analysis of obesogenic effects in invertebrates is limited by our poor knowledge of the regulatory pathways of lipid metabolism.TBT's disruptive effects translated into a lower fitness for offspring and adults.These findings indicate the presence of obesogenic effects in a nonvertebrate species.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research (IDAEA), Spanish Research Council (IDAEA, CSIC), Barcelona, Spain.

ABSTRACT

Background: The analysis of obesogenic effects in invertebrates is limited by our poor knowledge of the regulatory pathways of lipid metabolism. Recent data from the crustacean Daphnia magna points to three signaling hormonal pathways related to the molting and reproductive cycles [retinoic X receptor (RXR), juvenile hormone (JH), and ecdysone] as putative targets for exogenous obesogens.

Objective: The present study addresses the disruptive effects of the model obesogen tributyltin (TBT) on the lipid homeostasis in Daphnia during the molting and reproductive cycle, its genetic control, and health consequences of its disruption.

Methods: D. magna individuals were exposed to low and high levels of TBT. Reproductive effects were assessed by Life History analysis methods. Quantitative and qualitative changes in lipid droplets during molting and the reproductive cycle were studied using Nile red staining. Lipid composition and dynamics were analyzed by ultra-performance liquid chromatography coupled to a time-of-flight mass spectrometer. Relative abundances of mRNA from different genes related to RXR, ecdysone, and JH signaling pathways were studied by qRT-PCR.

Results and conclusions: TBT disrupted the dynamics of neutral lipids, impairing the transfer of triacylglycerols to eggs and hence promoting their accumulation in adult individuals. TBT's disruptive effects translated into a lower fitness for offspring and adults. Co-regulation of gene transcripts suggests that TBT activates the ecdysone, JH, and RXR receptor signaling pathways, presumably through the already proposed interaction with RXR. These findings indicate the presence of obesogenic effects in a nonvertebrate species.

No MeSH data available.